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Is Energy Conserved?

There exists a phenomenon in space that explains the red and blue shift observed by astronomers when they look at distant galaxies receding away from us or moving towards us. This phenomenon is more accurately known as the CosmologicalDoppler effect.

Imagine a part of the Electro Magnetic spectrum coming to us from a distant galaxy. Since the wavelength and the frequency of this wave change as it moves through space, it can be argued by Plank's hypothesis that the energy i.e. \(h\nu\) is continuously changing, or more specifically decreasing, due to the expansion of the fabric of space-time.

So, is it true that it can be said the energy, in this case, is lost?

TrueFalseDepends on the wavelength usedDepends on the rate of expansion of the Universe.